If a telecommunications service is to remain reliable over a long period all conductors and connectors must be protected from the environment, particularly from moisture. A problem therefore arises where cables are spliced together or where drop wires are spliced into a cable, since the conductors must be exposed in order to make the desired electrical connections. Any cable jacket or insulation removed for this purpose must therefore be made good after the electrical connections have been made. Analogous problems arise in the case of optical fibre cables, and the present invention applies to them also.
In general, telecommunications cable splices are protected from the environment by building around them a so-called splice case or splice enclosure. The design of such an enclosure will depend upon the nature of the cables or drop wires to be spliced, on the severity of the environment and on the position of the splice in the telecommunications network. In the present case we are particularly, although not exclusively, concerned with a closure for butt splices in the aerial distribution network that can readily be re-entered, and that can be installed without special tools, particularly without a source of heat (as is required for widely used heat-shrinkable enclosures and enclosures employing hot-melt adhesives).
Various prior art splice enclosures will now be referred to. In each case a butt splice is enclosed by an enclosure comprising a base and a dome-like cover.
EP 0094848 (Raychem) discloses an enclosure suitable as a telecommunications radial distribution point comprising a base having at least three passages and a cover which fits over one side of the base. The passages are provided with at least one tubular recoverable outlet on one side of the base and at least one tubular recoverable outlet on the other side of the base. Reference may also be made to GB 2104313 (Raychem).
U.S. Pat. No. 3,728,467 (Klayum et al) discloses a buried-type ready-access splice closure comprising a dielectric base with a pair of openings for receiving the opposite runs of a loop of cable. The base is split along a parting region that passes through the centres of the openings. The base also has clamping means for clamping the runs of cable and for grounding the shield of the cable outside of the base. The loop of cable has its coverings stripped away to expose the insulated core wires for splicing to service (ie-drop) wires. The loop is supported by a bracket that is attached to the base and to the clamping means, and the loop and bracket are enclosed by a cover that is removably clamped to the base.
U.S. Pat. No. 3,557,299 (Dienes) discloses a device for making tap connections to continuous cable wherein a loop of the cable, with insulated conductors exposed for connection, is brought through a tightly fitting rubbery sleeve into a connection area which is thereafter hermetically sealed. Clamps are provided which support the cable rigidly in position with respect to a base and an elastic sleeve which fits into an opening in the base. A dome-shaped cover is fitted over the base.
U.S. Pat. No. 3,848,074 (Channell) discloses a terminal and splice enclosure for cables, including an annular terminal base on which is threaded a cover, a resilient sealing and locking band secures the cover on the base. The base has a tapered opening which receives a tapered grommet having variable size holes through which the cables pass in sealed relationship.
Two instances of prior art in-line, rather than butt, splice closures will be mentioned in view of the cable end seals that are disclosed.
U.S. Pat. No. 4,701,574 (Shimirak et al.) discloses a cable end seal, and a closure which includes the cable end seal, the end seal providing a barrier against water. First and second end seals are disposed adjacent opposite sides of a cable splice, and placed in compression around the cable, the end seals having outer convoluted surfaces which mate with a variable length convoluted tubing bridging member so as to form an environmental closure for the splice. The end seals are split and have an axial bore to allow passage of a cable therethrough. Preferably the end seals comprise a gel having an open loop network such that it is elastic, conformable and has a cone penetration preferably between 80 and 350 (10.sup.-1 mm) and an ultimate elongation in excess of 50%, the gel being contained within a member having a plurality of convolutions therearound. Attention is also directed to U.S. Pat. No. 4,880,676 (Puigcerver et al) which also discloses cable splice case end seals. Here a gel is used having a cone penetration value from 50 to 200 (10.sup. -1 mm) and an ultimate elongation of at least 50% and it is provided in a casing that at least partially surrounds the gel and that has an external circumferentially-extending convolution. The casing has an aperture, through the thickness thereof through which the gel extends to contact circumferentially-extending gel at an external surface of the case.
PCT GB 8901336 (Raychem) discloses a method of environmentally protecting an elongate substrate, such as a cable splice, with a cover and a sealing means having an elongation of at least 100% and a compression set at 70.degree. C. of less than 30% which comprises positioning the sealing means around a portion of the substrate and surrounding the substrate with the cover such that the sealing material provides a seal between the cover and the substrate. The sealing means may comprise a sealing material such as a gel in substantially rigid parts that are held together by means such as screws. The parts are separable and together define holes through which the substrates to be sealed will pass. Also disclosed is a device that may be secured to a sealing means to provide an enclosure with mechanical strength for example axial-pull strength or with electrical earth continuity. Armour or other strength member of the cables to be spliced may be secured to a flange or other part of the device by securing means such as a bolt.